1. Field of the Invention
The present invention relates to a thin-film magnetic head provided with a magnetoresistive (MR) element, and more particularly to a thin-film magnetic head in which a crystallized layer is not formed on the surface of a shielding layer facing a MR element, magnetic properties are not degraded, and the effective gap length can be easily controlled.
2. Description of the Related Art
As thin-film magnetic heads provided with magnetoresistive elements (MR elements), anisotropic magnetoresistive (AMR) heads using an anisotropic magnetoresistance effect and giant magnetoresistive (GMR) heads using the spin-dependent scattering phenomenon of conduction electrons have been known. As an example of the GMR head, a spin-valve head in which a high magnetoresistance effect is exhibited in a small external magnetic field is disclosed in U.S. Pat. No. 5,159,513.
FIG. 19 is a schematic diagram which shows the structure of a conventional AMR head. In the conventional AMR head, an insulating layer 8 as a lower gap layer is formed on a lower shielding layer 7 composed of a magnetic alloy having the crystal structure of Sendust (Fexe2x80x94Alxe2x80x94Si) or the like. An AMR element 10 is deposited on the insulating layer 8. In the AMR element 10, a nonmagnetic layer 12 is formed on a soft magnetic layer 11, and a ferromagnetic layer (AMR material layer) 13 is further formed on the nonmagnetic layer 12. Magnetic layers 15 are formed at both sides of the AMR element 10, and conductive layers 16 are formed on the magnetic layers 15. Furthermore, an insulating layer 18 as an upper gap layer is formed, and an upper shielding layer 19 is formed thereon.
In the AMR head having the structure described above, in order to prevent a rise in the temperature of the AMR element 10 due to heat generated by a steady-state sensing current, which may vary the electrical resistance of the ferromagnetic layer 13, the upper and lower gap layers 8 and 18 are composed of alumina (Al2O3), and heat generated by the steady-state sensing current is gradually transmitted through the gap layers 8 and 18 to the shielding layers 7 and 19, and thus the heat is dissipated.
In order to optimally operate such an AMR head, two bias magnetic fields must be applied to the ferromagnetic layer 13 which exhibits an anisotropic magnetoresistance effect.
A first bias magnetic field is used to make a change in the resistance of the ferromagnetic layer 13 linearly responsive to a magnetic flux from a magnetic medium. The first bias magnetic field is applied perpendicular to the surface of the magnetic medium (in the Z direction in FIG. 19) and parallel to the plane of the ferromagnetic layer 13. The first bias magnetic field is usually referred to as a lateral bias. The soft magnetic layer 11 is magnetized in the Z direction by a magnetic field induced by a sensing current that is conducted by conductive layers 16 though the AMR element 10, and a lateral bias is applied to the ferromagnetic layer 13 in the Z direction by the magnetization of the soft magnetic layer 11.
A second magnetic field is usually referred to as a longitudinal bias, and is applied parallel to the magnetic medium and the plane of the ferromagnetic layer 13 (in the X direction in FIG. 19). The longitudinal bias is applied so that Barkhausen noise, which is caused due to many domains formed in the ferromagnetic layer 13, is suppressed, namely, a smooth change in resistance with decreased noise in response to the magnetic flux from the magnetic medium is enabled.
In order to suppress Barkhausen noise, the ferromagnetic layer 13 must be aligned in a single-domain state. There are two known methods for applying the longitudinal bias. In the first method, the magnet layers 15 are disposed at both sides of the ferromagnetic layer 13 and a leakage flux from the magnet layers 15 is used. In the second method, an exchange anisotropic magnetic field produced at the contact interface between an antiferromagnetic layer and a ferromagnetic layer is used.
As a GMR head in which exchange anisotropic magnetic coupling by an antiferromagnetic layer is used, a spin-valve type GMR head shown in FIG. 20 is known.
The GMR head shown in FIG. 20 differs from the AMR head shown in FIG. 19 in a GMR element 20 which is provided instead of the AMR element 10.
The GMR element 20 includes a free ferromagnetic layer 22, a nonmagnetic intermediate layer 23, a pinned ferromagnetic layer 24, and an antiferromagnetic layer 25.
In the structure shown in FIG. 20, the free ferromagnetic layer 22 must be magnetized in the track width direction (in the X direction in FIG. 20) while the free ferromagnetic layer 22 is aligned in a single-domain state by applying a bias in the track width direction by the magnet layers 15, and the pinned ferromagnetic layer 24 must be magnetized in the Z direction in FIG. 20 while the pinned ferromagnetic layer 24 is aligned in a single-domain state by applying a bias in a direction perpendicular to the magnetization direction of the free ferromagnetic layer 22. That is, the magnetization direction of the pinned ferromagnetic layer 24 should not be changed by the magnetic flux from a magnetic medium (in the Z direction in FIG. 20), and the linear responsiveness of the magnetoresistance can be obtained by a change in the magnetization direction of the free ferromagnetic layer 22 within a range of 90xc2x1xcex8xc2x0 in relation to the magnetization direction of the pinned ferromagnetic layer 24.
A relatively large bias magnetic field is required in order to pin the magnetization of the pinned ferromagnetic layer 24 in the Z direction in FIG. 20, and the larger the better. A bias magnetic field of at least 100 Oe is required in order to overpower a demagnetizing field in the Z direction and to prevent the magnetization direction from being influenced by the magnetic flux from the magnetic medium. As a method for generating the bias magnetic field, in the structure shown in FIG. 20, an exchange anisotropic magnetic field, which is produced by providing the antiferromagnetic layer 25 in contact with the pinned ferromagnetic layer 24, is used.
Accordingly, in the structure shown in FIG. 20, since the magnetization of the pinned ferromagnetic layer 24 is pinned in the Z direction by exchange anisotropic coupling produced by providing the antiferromagnetic layer 25 in contact with the pinned ferromagnetic layer 24, when a fringing magnetic field is applied from a magnetic medium moving in the Y direction, the electrical resistance of the GMR element 20 is changed in response to a change in the magnetization direction of the free ferromagnetic layer 22, and thus the fringing magnetic field from the magnetic medium can be detected by the change in the electrical resistance.
A bias applied to the free ferromagnetic layer 22 secures the linear responsiveness and suppresses Barkhausen noise resulting from the formation of many domains. A similar method to that of the longitudinal bias in the AMR head is employed in the structure shown in FIG. 20. That is, magnetic layers 15 are provided at both sides of the free ferromagnetic layer 22, and a leakage flux from the magnetic layers 15 is used as a bias.
With respect to the conventional thin-film magnetic heads, since the lower shielding layer 7 is composed of a magnetic alloy having the crystal structure of Fexe2x80x94Alxe2x80x94Si (Sendust), Nixe2x80x94Fexe2x80x94Nb, or the like, the surface of the lower shielding layer 7 is uneven. Thereby, if a MR element is formed on the lower shielding layer 7 with the thin lower gap layer 8 having a thickness of approximately 550 angstroms therebetween, unevenness and pin holes may occur in the surface of the MR element. The unevenness and the like occurs in the surface of the MR element because the MR element, which comprises a laminate including thin films, is as thin as 0.03 xcexcm and is easily influenced by the surface roughness of layers below the MR element.
Recently, there is an increased demand for further improving the shielding characteristics of thin-film magnetic heads, and for that purpose, as the material for the upper and lower shielding layers 7 and 18, a material having more sophisticated characteristics than those of Fexe2x80x94Alxe2x80x94Si (Sendust) or Nixe2x80x94Fexe2x80x94Nb must be used.
Accordingly, use of amorphous magnetic alloy films composed of Co87Zr4Nb9 as the material for shielding layers has been researched, in which excellent shielding characteristics are exhibited and planar surfaces can be obtained.
When a thin-film magnetic head is fabricated, after an amorphous magnetic alloy film composed of Co87Zr4Nb9 is deposited on a substrate, the lower shielding layer 7 is formed by annealing and photolithography. Next, after exposure to the atmosphere, an Al2O3 film as the lower gap layer 8 is deposited on the lower shielding layer 7. It has been found that if the lower shielding layer 7 comprises the amorphous magnetic alloy film composed of Co87Zr4Nb9, while the lower shielding layer 7 and the lower gap layer 8 are formed, an oxide layer of Zr, Nb, etc, is formed on the surface of the lower shielding layer 7 (the surface facing the MR element) and a high Co-concentration layer having a higher Co concentration than that of the rest of the layer is further formed therebelow. When the lower shielding layer 7 has a design thickness of approximately 1 xcexcm, the thicknesses of the oxide layer and the high Co-concentration layer are approximately 30 angstroms and 30 to 100 angstroms, respectively. The observation of the high Co-concentration layer by a high-resolution transmission electron microscope (TEM) has confirmed that a crystallized layer has been formed.
In the thin-film magnetic head having the structure described above, since the lower shielding layer 7 lies adjacent to the MR element with the lower gap layer 8 therebetween, the magnetic properties of the outermost surface of the lower shielding layer 7 are particularly important. If the oxide layer and the crystallized layer are on the surface of the lower shielding layer 7 facing the MR element, the magnetic properties of the surface of the lower shielding layer 7 facing the MR element deteriorate, and the regenerated waveforms and the waveform symmetry (asymmetry) of the thin-film magnetic head may become unstable. If the crystallized layer is on the surface of the lower shielding layer 7 facing the MR element, the surface becomes uneven, and unevenness and pinholes may occur in the surface of the MR element.
The thickness of an insulating layer between the MR element and the lower shielding layer 7 corresponds to a gap length, and the thickness of the lower gap layer 8 is set according to the gap length. However, if the oxide layer and the crystallized layer are included in the lower shielding layer 7, the effective gap length is increased to a length corresponding to the thickness of the lower gap layer 8 plus the thicknesses of the oxide layer and the crystallized layer, resulting in a difficulty in controlling the effective gap length, which is disadvantageous in terms of head design.
Accordingly, it is an object of the present invention to provide a thin-film magnetic head in which a crystallized layer is not formed on the surface of a shielding layer facing a MR element, magnetic properties are prevented from deteriorating, and the effective gap length can be easily controlled.
In the present invention, a thin-film magnetic head includes a magnetoresistive element, a shielding layer, and an insulating layer disposed between the magnetoresistive element and the shielding layer. The shielding layer is composed of an amorphous material and the surface thereof facing the magnetoresistive element is covered by a crystallization-inhibiting film for inhibiting crystallization of the shielding layer.
In the thin-film magnetic head of the present invention, the crystallization-inhibiting film for the shielding layer is formed on the surface of the amorphous shielding layer facing the magnetoresistive element. After the shielding layer is deposited, the crystallization-inhibiting film is formed on the shielding layer continuously or after short exposure to the atmosphere, and the insulating layer is deposited on the crystallization-inhibiting film. Since the surface of the shielding layer facing the magnetoresistive element is covered by the crystallization-inhibiting film, the shielding layer is not brought into contact with oxygen for a long period of time, and thereby a change in the quality of the shielding layer can be avoided and the formation of a crystallized layer on the surface of the shielding layer facing the magnetoresistive layer can be avoided.
In the thin-film magnetic head of the present invention, preferably, the crystallization-inhibiting film for the shielding layer has an antioxidizing function for the shielding layer. In such a thin-film magnetic head, even if the crystallization-inhibiting film and the insulating layer are deposited in that sequence in a manner similar to that described above, since the surface of the shielding layer facing the magnetoresistive element is covered by the crystallization-inhibiting film having the antioxidizing function, the shielding layer is not brought into contact with oxygen for a long period of time, a change in the quality of the shielding layer can be avoided, the formation of an oxide layer composed of ingredients of the shielding layer on the surface of the shielding layer facing the magnetoresistive element can be inhibited, and the formation of a crystallized layer can be avoided.
Accordingly, in the thin-film magnetic head of the present invention, the formation of a crystallized layer on the surface of the shielding layer facing the magnetoresistive element can be avoided, or the formation of both an oxide layer composed of ingredients of the shielding layer and a crystallized layer can be inhibited. Thereby, the magnetic properties of the surface of the shielding layer facing the magnetoresistive element are prevented from deteriorating, and the stability of regenerated waveforms as well as the stability in the waveform symmetry (asymmetry) can be improved.
Since the crystallized layer is not formed on the surface of the shielding layer facing the magnetoresistive element, the surface facing the magnetoresistive element is planar, and unevenness and pinholes do not occur in the surface of the magnetoresistive element formed on the shielding layer with the insulating layer therebetween, and thus a planar surface can be obtained.
In the present invention, since the formation of the crystallized layer on the surface of the shielding layer facing the magnetoresistive element can be avoided, or the formation of both the oxide layer of ingredients of the shielding layer and the crystallized layer can be inhibited, the effective gap length depends on only the thicknesses of the insulating layer between the magnetoresistive element and the shielding layer and the crystallization-inhibiting film for the shielding layer. Thereby, the effective gap length can be easily controlled by controlling the thicknesses of the insulating layer and the crystallization-inhibiting film. For example, when a high-melting point metal layer is deposited on the surface of the shielding layer facing the magnetoresistive element at a thickness of X angstroms using a high-melting point metal selected from the group consisting of Ta, W, and Hf as the material for the crystallization-inhibiting film for the shielding layer, the thickness of the high-melting point metal layer is reduced by 10 angstroms, and the high-melting point layer at a thickness of Xxe2x88x9210 angstroms is formed on the shielding layer, and a metal oxide layer at a thickness of 20 angstroms is formed on the high-melting point metal layer (on the insulating layer side). Thereby, the effective gap length corresponds to the thickness of the insulating layer plus X+10 angstroms. Consequently, when the effective gap length is set at a predetermined length (Y angstroms), by depositing the insulating layer at a preliminarily reduced thickness, i.e., at a thickness of Yxe2x88x92(X+10), the predetermined effective gap length can be obtained, and thus the effective gap length can be easily controlled.
Moreover, if the crystallization-inhibiting film is formed on the shielding layer, since water-cleaning can be employed after the photolithography process, the usage of an organic solvent-based cleaning agent can be reduced.
In the thin-film magnetic head of the present invention, as the material for the crystallization-inhibiting film, at least one material selected from the group consisting of Ta, W, Hf, Al2O3, SiO2, and Ta2O5 may be used. Among them, preferably, at least one high-melting point metal selected from the group consisting of Ta, W, and Hf, is used, which forms a strong, thin passivation layer, does not easily diffuse into the shielding layer even in the annealing process and the like, and has a melting point higher than that of the material constituting the insulating layer.
In the thin-film magnetic head using the high-melting point metal as the material for the crystallization-inhibiting film, the shielding layer is deposited and the crystallization-inhibiting film is formed on the shielding layer continuously or after short exposure to the atmosphere, and then the insulating layer is deposited on the crystallization-inhibiting film. Thus, an oxide layer of the metal is formed on the insulating layer side and the surface of the shielding layer facing the magnetoresistive element is covered by the high-melting point metal layer. Since the shielding layer is not brought into contact with oxygen for a long period of time, and the ingredient of the crystallization-inhibiting film does not diffuse into the shielding layer, a change in the quality of the shielding layer can be avoided, and the formation of the oxide layer and the crystallized layer composed of the ingredients of the shielding layer on the surface of the shielding layer facing the magnetoresistive layer can be avoided.
In the magnetic head in which at least one oxide selected from the group consisting of Al2O3, SiO2, and Ta2O5 is used as the material for the crystallization-inhibiting film, the shielding layer is deposited and the crystallization-inhibiting film is formed on the shielding layer continuously or after short exposure to the atmosphere, and then the insulating layer is deposited on the crystallization-inhibiting film. Thus, an oxide film (a film containing oxygen) is interposed between the shielding layer and the insulating layer. However, since oxygen in the oxide film is stabilized, the oxygen does not attack the shielding layer, and also since the surface of the shielding layer facing the magnetoresistive element is covered by the stable crystallization-inhibiting film, the shielding layer is not brought into contact with oxygen in air. Thereby, a change in the quality of the shielding layer can be avoided, and the formation of the oxide layer and the crystallized layer composed of the ingredients of the shielding layer on the surface of the shielding layer facing the magnetoresistive element can be avoided.
Moreover, in the thin-film magnetic head of the present invention, the crystallization-inhibiting film may include a high-melting point metal layer formed on the shielding layer side and an oxide layer formed on the insulating layer side. The high-melting point metal layer may be composed of at least one metal selected from the group consisting of Ta, W, and Hf, and the oxide layer may be composed of at least one oxide selected from the group consisting of Al2O3, SiO2, and Ta2O5.
In the thin-film magnetic head having such a structure, the shielding layer is deposited and the crystallization-inhibiting film is formed on the shielding layer continuously or after short exposure to the atmosphere, and then the insulating layer is deposited on the crystallization-inhibiting film. Thus, the oxide layer is formed on the insulation layer side and the surface of the shielding layer facing the magnetoresistive element is covered by the high-melting point metal layer. Since the shielding layer is not brought into contact with oxygen for a long period of time and the ingredient of the crystallization-inhibiting film does not diffuse into the shielding layer, a change in the quality of the shielding layer can be avoided and the formation of the oxide layer and the crystallized layer composed of the ingredients of the shielding layer on the surface of the shielding layer facing the magnetoresistive element can be avoided.
Preferably, the thickness of the crystallization-inhibiting film is 20 angstroms or more. If the thickness of the crystallization-inhibiting film is less than 20 angstroms, the effect of inhibiting the formation of a crystallized layer on the surface of the shielding layer facing the magnetoresistive element becomes insufficient.
When the high-melting point metal is used as the material for the crystallization-inhibiting film, the high-melting point metal layer is preferably formed at a thickness of more than 10 angstroms. The reason for this is that, when the shielding layer is deposited and the high-melting point metal layer having a thickness of 10 angstroms or less and the insulating layer are deposited in that sequence on the shielding layer continuously or after short exposure to the atmosphere, the thickness of the high-melting point metal layer is reduced by 10 angstroms, and the oxide layer of the high-melting point metal with a thickness of 20 angstroms is formed. That is, the surface of the shielding layer facing the magnetoresistive element is covered by the oxide layer of the high-melting point metal, and in comparison with the case in which the surface facing the magnetoresistive element is covered by the high-melting point metal layer, the effect of inhibiting the formation of the oxide layer and the crystallized layer composed of the ingredients of the shielding layer on the surface facing the magnetoresistive element is weakened.
Furthermore, in the thin-film magnetic head of the present invention, preferably, the thickness of the crystallization-inhibiting film is one tenth or less of that of the insulating layer. Since the distribution of the thickness of the insulating layer varies by approximately xc2x110%, if the thickness of the crystallization-inhibiting film adjacent to the insulating layer is within the above range of variation, the gap length is not greatly affected. If the thickness of the crystallization-inhibiting film exceeds the one tenth of the thickness of the insulating layer, the thickness of the insulating layer is reduced by just that much, and the effect of preventing the leakage of the current flowing through the magnetoresistive element is decreased.
In the thin-film magnetic head of the present invention, the distance between the shielding layer and the magnetoresistive element is preferably larger than a thickness corresponding to the thickness of the insulating layer plus 20 angstroms.
If the distance between the shielding layer and the magnetoresistive element is less than a thickness corresponding to the thickness of the insulating layer plus 20 angstroms, the thickness of the crystallization-inhibiting film also becomes less than 20 angstroms. Thereby, the effect of inhibiting the formation of the crystallized layer on the surface of the shielding layer facing the magnetoresistive element becomes insufficient.